Booklets, etc. of the kind described in the introduction are already known in many embodiments. Examples of such booklets and how they are manufactured and used are to be found inter alia in the U.S. Pat. No. 3,973,787, 4,129,471, 4,289,330 and 4,367,061.
In the last-mentioned specification there is described and illustrated how a glue strip is attached to the inside of the booklet spine substantially simultaneously with crease lines being formed on either side of the strip, this giving, inter alia, the advantage that the glue strip is very carefully oriented between the crease lines, whereby folding the booklet along them can be performed without obstruction from the glue strip, and it is ensured at the same time that the edges of all the sheets of paper later inserted in the booklet are joined to the melted glue strip along the entire length of the spine, while at the same time the booklet in the area of the glue strip is given, both inside and outside, a high-quality implementation without irregularities and other deficiencies deleterious to its appearance.
A disadvantage burdening the booklet according to the U.S. Pat. No. 4,367,061 is, however, that outside sheets in a sheaf which is inserted in the booklet for joining to the inside of the booklet spine may come between the glue strip and the covers, particularly for the reason that the covers are not usually parallel, but diverge from the spine. This results in at least the outer sheets not completely coming into contact with the glue strip during the binding operation, in turn resulting in that they can come loose from the finished booklet.
To remove the disadvantage mentioned in the previous paragraph it has been proposed to apply binder and/or guide means on the insides of the covers in the vicinity of the creasing lines between the covers and the spine, as is illustrated in the three first-mentioned of the cited U.S. patent specifications, thus to ensure that all sheets in the sheaf will come into engagement against the strip on the spine. In the case where binding agent is used for this purpose, only the two outmost sheets in the sheaf will be joined to it, while the next outmost sheets and possibly further sheets in the sheaf which have come outside the glue strip will not be bound. Furthermore, the use of binding agent on the covers means an increased cost and a more complicated manufacturing method. In the case where guide means are used, the available space between the covers is decreased and an unutilised gap occurs on either side of the sheaf. In the case where the binding agent on both covers and on the strip forms a cohesive band, creasing along the creasing lines or their preparation is made more difficult as well as there being the consumption of an unnecessary large amount of binding agent.